This application claims the priority of German patent Application No. 199 27 669.2 filed Jun. 17, 1999, which is incorporated herein by reference:
The valve drives of piston-type internal combustion engines with fully variable actuation of the cylinder valves are electromagnetic actuators that each essentially comprises two electromagnets that are axially spaced from each other. An armature that is connected to the respective cylinder valve moves back and forth between the two electromagnets. The current supply to the electromagnets is controlled by an engine control unit. For the actuator operation, it is furthermore important that the impact speed of the armature on the pole surface of the associated electromagnet is minimized once the respective switching position is reached, in that a safe operation with simultaneous minimizing of the electrical power consumption is critical. The actuators therefore cannot be operated without integrated sensors in order to meet the operational requirements of the piston-type internal combustion engine. However, the existence of such sensors leads to possible malfunctions that must be monitored. Important in this connection is the failure of a sensor while the associated actuator is still operational. Until now, the failure of a sensor on an actuator resulted in the respective actuator being identified as xe2x80x9cnon operativexe2x80x9d by the engine control unit. Accordingly, the associated cylinder is completely shut down by turning off the fuel supply and preventing the firing of the cylinder. Depending on the case, the actuators for all cylinder valves of this cylinder may also be shut down. If necessary, the load share of the malfunctioning, shutdown cylinder is then distributed, via corresponding control programs in the engine control unit, to the other fired cylinders.
In accordance with the invention, the above discussed problems are corrected by a method for monitoring the operation of a piston-type internal combustion engine with fully variable actuation of the electromagnetic actuator for the cylinder valves, which can be actuated by an engine control unit that controls a current supply based on respective predetermined current flows. The cylinder valves are each associated with a respective sensor for detecting the actuator operation, which sensor transmits relevant signals for the movement curve of the respective actuator to the engine control unit, wherein the current flow and voltage course or curve for the actuator are detected. The lack of a sensor signal, indicating a sensor failure or a failure of the actuator, is detected by use of the voltage curve at the actuator. If a sensor of an actuator fails, the detection of a sensor signal is taken up by the engine control unit from the sensor of another corresponding actuator. The engine control unit then switches to the starting operation for the actuator initially identified as non operative (start of oscillations), and does not shut down the associated cylinder until a failure of this actuator is detected.
With a failed sensor but still operative actuator, this measure allows continued operation of the piston-type internal combustion engine with a normal operational sequence for all cylinders and the replacement of the failed or missing sensor signal with a signal from an operative sensor on another, corresponding actuator. However, if the detection of current and voltage during the movement sequences should show that no armature movement is occurring, then damage to the actuator must be assumed and the cylinder must be shut down accordingly. This means that the fuel supply is shut down, the cylinder is not fired and continues to operate xe2x80x9cempty,xe2x80x9d depending on the layout of the program and the number of cylinder valves that are provided. The remaining cylinder valves are actuated in the normal operating cycle. It may be advisable in that case if at least the fuel supply to the respective cylinder already is shut down during the test phase, meaning during the transition to the starting operation, and is started again only after the signal xe2x80x9cactuator operationalxe2x80x9d has been received. As a result, the travel of non-burnt fuel during this intermediate phase into the exhaust-gas system, where it loads the exhaust gas post-processing equipment with non-burnt hydrocarbons, is avoided.
A modified version of the method according to the invention provides that for start-up and/or normal operation, the actual current flow for the actuator that corresponds to the actuator with a defective sensor is stored in the engine control unit and is expanded or changed by increased factors of safety for the progression over time and/or the current level, and the actuator with a defective sensor is actuated based on the expanded or changed current flow. In case of a sensor failure but an otherwise functional actuator, it is thus possible to take into account external influences that may be present, for example, a stray band caused by the combustion stochastic, straying in the actuator characteristic or even possible actuator wear. The expansion of the current flow in particular can result in an increase in the level of the capturing current and/or in moving forward the time for activating the capturing current, so as to ensure a successful start-up via such an increased factor of safety.
A modification of the invention provides for the engine control unit to detect, as a corresponding actuator, the operation of an actuator operated according to the control program under the same operating conditions as the actuator to be started. For an actuator with a sensor defect on a gas intake valve, this means that the actuator of another gas intake valve is considered as a corresponding actuator. The same is true for the gas discharge valves. For a piston-type internal combustion engine whose the respective cylinders have at least two gas intake valves and/or at least two gas discharge valves, it is advantageous if the actual current flow to be stored is detected from the corresponding actuator on the same cylinder. With piston-type internal combustion engines having, for example, two intake valves but only one discharge valve or with piston-type internal combustion engines having only one intake valve and one discharge valve for each cylinder, the current flow to be stored for the actuator with a sensor defect on this one valve is tapped or picked up from a corresponding actuator on another cylinder.
The realization of the method according to the invention furthermore provides that in order to take into account the engine dynamics, the actual current flow selected is that of a corresponding actuator on a cylinder that is positioned in the firing sequence directly in front of the cylinder having the actuator with the sensor defect. As a result, the actuation of the actuator with a failed sensor can be taken over by the sensor of the corresponding actuator without noticeable effect on the engine operation.
In addition, the realization of the method according to the invention provides that as an increased factor of safety for the current flow to be expanded, only a displacement of the opening time in the direction of a xe2x80x9clate discharge openingxe2x80x9d is made on an actuator with a sensor defect in order to actuate the discharge valve. For this, the actuator is operated on the basis of the normal current flow, predetermined by the control unit, with respect to the capturing current level and also the capturing current start-up time. The actuator is actuated only with a somewhat later control time for the discharge opening because the pressure level in the associated cylinder has already dropped and the operation is therefore safer.
The invention is explained in further detail below with the aid of schematic drawings.